We would never have signed Arteta, Pienaar or a number of other players if we solely judged them on what they did at their previous clubs.
Considering how highly he was rated before he signed for Man Utd and how good he looked in Holland (yes, usual caveat about Dutch league applies), a loan with a view to buy makes perfect sense. Worst case scenario - you have a crap player on loan for 6 months. We've had plenty of those - in fact we've got one right now. Best case scenario - player performs to his potential, we sign him for the agreed fee and we have a young, quality player.